Network cameras (also known as IP cameras) are becoming increasingly popular in surveillance applications. The term “network camera” is used in the context of the present patent application and in the claims to refer to a self-contained video device that outputs a sequence of data packets containing digitized image data. Such cameras contain not only a video sensor and associated video electronics, but also digital processing circuitry and a packet network interface with the necessary hardware and software to plug in directly to a packet communication network, such as an Ethernet local area network (LAN). Network cameras are particularly convenient for security applications, because they can be deployed freely in and around a facility using the existing LAN infrastructure, rather than requiring dedicated cabling to be run to each camera as in traditional video security systems.
A growing number of manufacturers supply network cameras. Axis Communications (Lund, Sweden), for example, sells a line of network cameras that may be used in embodiments of the present invention that are described hereinbelow.
In a computer network handling sensitive data, such as data in military or financial environments, portions of the network may be connected by one-way links. The term “one-way link” is used in the context of the present patent application and in the claims to refer to a communication link that is physically configured to carry signals in one direction and to be incapable of carrying signals in the opposite direction. For example, confidential data that must not be accessed from external sites may be stored on a computer that is configured to receive data over a one-way link and has no physical outgoing link over which data might be transmitted to the external site.
One-way links may be implemented, for example, using Waterfall™ systems, which are manufactured by Gita Technologies, Ltd. (Rosh HaAyin, Israel). The Waterfall system provides a physical one-way connection based on fiberoptic communication, using an underlying proprietary transfer protocol. When a transmitting computer is connected by a Waterfall system (or other one-way link) to a receiving computer, the receiving computer can receive data from the transmitting computer but has no physical means of sending any return communications to the transmitting computer.